Perhaps also why they fought Keystone (pipeline) so long! Perhaps KEYSTONE pipeline path intersects/interrupts trafficking routes and/or brings unwanted eyes and ears to the area!
High tech pipeline monitors might pickup underground tunnel travel as well as overland travel?
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The misdirection idea is interesting.... as is the one above.
In addition, they may be working to seal off the Mexico border, as challenging as that is politically, to set the precedent. We have had traditionally a concept of no problems at the Canadian border overall. Right now there is not the political will to tackle closing it off. There is a LOT of political will to close the Mexican border. Get that southern border under control - show it can be done, then work on plugging the other leaks.
I had had no idea that the Canadian border was so horrible. Definitely had to swallow a red pill with that crumb.
In New York State alone there is the St. Lawrence River with miles and miles of shoreline and thousands of people on both sides. There's a reason why you see many very fast boats in that waterway.